Targeted at learning about pathogenic processes of inflammatory eye diseases, this project focused in FY 2013 on the following four issues detailed below: (1) Both spleen and lungs are involved in the process of licensing sensitized CD4 cells to acquire pathogenicity A recent paper in Nature (Odoardi et al, 2012, 488:675-9) provided data indicating that the lung is the only organ to which pre-sensitized T-lymphocytes home to in order to be licensed for acquisition of pathogenic capacity. The reported data were collected only with in vitro sensitized T-cells, adoptively transferred into nave recipient animals. To examine the authors conclusion in a physiological system, we used an experimental system we developed in which nave CD4 cells specific against hen egg lysozyme (HEL) are adoptively transferred into recipients expressing HEL in their eyes. Treatment of the recipient mice with Toll-like receptor (TLR) ligands stimulates the donor cells to acquire pathogenicity and induce ocular inflammation. Tracing the nave donor cells (by a clonotypic antibody) revealed that the kinetics of migration into, proliferation in, and exit of donor cells out of the spleen closely resemble those in the lung. Moreover, we tested in this system two TLR ligands, endotoxin (lipopolysaccharide, LPS) and the oligodeoxynucleotide CpG, and found that the process of activation by CpG is faster than that induced by endotoxin and the faster kinetics was observed with cells homing to either the spleen or the lungs. We conclude, therefore, that the spleen shares with the lung the presumed function of licensing sensitized T-cells to acquire pathogenicity. Furthermore, since the total number of donor cells homing to the spleen is substantially larger than the number homing to the lungs, it seems that in the mouse, the spleen plays a major role in the licensing process. (2) A new animal model for allergic conjunctivitis Our study with T-helper cells selectively expressing IL-9 (Th9 cells)(initially reported in FY-2010) was extended in FY-2013 by testing the enhancing effect of the TNF-like cytokine, TL1A, on the generation of Th9 lineages. TL1A enhanced remarkably the acquisition of Th9 phenotype by nave CD4 cells, as well as the pathogenicity of the generated Th9 cells, i.e., their capacity to induce ocular inflammation in eyes expressing the target antigen. Histological analysis of mouse eyes affected by the Th9 cells revealed that the inflammatory changes include intense accumulation of inflammatory cells in the conjunctiva. Furthermore, a substantial number of eosinophils, cells that are hallmark for allergic reaction, were identified among the cellular infiltrate in the conjunctiva. This observation is in line with the known involvement of IL-9 and Th9 cells in various allergic processes. Allergic conjunctivitis is a major eye disease in human and our study thus provides a new model for this condition. (3) The role of the LRRK2 gene in the development of experimental autoimmune uveitis (EAU) and related immune processes The leucine-rich repeat kinase 2 (LRRK2) gene has been identified by genome-wide association studies as being encoded by a major susceptibility gene for Crohn's disease, a condition assumed to be mediated by an autoimmune mechanism. A paper in Nature Immunology (Liu et al., 2011, 12:1063) reported that mice deficient in LRRK2 developed colitis with higher severity than their wild type controls. Testing LRRK2 deficient mice for their susceptibility to EAU revealed, however, that the ocular changes were less severe than those in wild type controls. Moreover, the immune response against the uveitogenic antigen (interphotoreceptor retinoid-binding protein) in LRRK2-deficient mice was inferior to that of the wild type controls. Analysis of expression of FoxP3, a transcription factor specific for regulatory T-cells indicated the LRRK2 deficient mice expressed slightly higher levels of this factor than their controls. (4) Investigating the capacity of Digoxin to suppress EAU and its toxicity to the retina. Digoxin, a compound used for treatment of certain heart conditions, was reported to also be immunosuppressive, capable of inhibiting the development of autoimmune condition such as experimental autoimmune encephalomyelitis (Huh et al., Nature, 2011, 472:486-90). Examining the capacity of Digoxin to inhibit EAU in mice revealed that this compound moderately suppressed the disease development. Unexpectedly, we also observed severe thinning of the retina in mice treated with Digoxin. Further histological analysis of the Digoxin-treated mouse eyes indicated that the toxic effect is apparent within six days and that it consists of remarkable reduction in the number of photoreceptor nuclei and drastic loss of outer segments, in particular in the peripheral retina.